[all-commits] [llvm/llvm-project] 678ded: [clang] Support for read-only types

[Malavika Samak via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 678ded017f21b22da3ab20ffafe2bc2dc4457493
      https://github.com/llvm/llvm-project/commit/678ded017f21b22da3ab20ffafe2bc2dc4457493
  Author: MalavikaSamak <malavika2 at apple.com>
  Date:   2022-12-15 (Thu, 15 Dec 2022)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Basic/Attr.td
    M clang/include/clang/Basic/AttrDocs.td
    M clang/include/clang/Basic/DiagnosticGroups.td
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/lib/Sema/SemaDecl.cpp
    M clang/lib/Sema/SemaDeclAttr.cpp
    M clang/test/Misc/pragma-attribute-supported-attributes-list.test
    A clang/test/Sema/attr-read-only-placement.cpp

  Log Message:
  -----------
  [clang] Support for read-only types

The main goal of this work is to allow developers to express the need to place instances
of a class or structure in the read-only part of the program memory. Such a placement is
desirable to prevent any further modifications to the instances of a given structure, by
leveraging the read-only run time protection.

To achieve this, we are introducing a new attribute that can be attached to any record
definition or a declaration. The compiler enforces that every instance of this type can
be placed in the read-only segment of the program memory, provided the target triplet
supports such a placement. If an instance of a given type bearing this attribute doesn’t
satisfy such a placement, the compiler attaches an appropriate warning at suitable program
locations. In other words, adding this attribute to a type requires every instance of this
type to be a global const, which are placed in the read-only segments for most target
triplets. However, this is *not a language feature* and it *need not* be true for
*all target triplets*.

The current patch emits a warning at global variable declaration sites of types bearing
the attribute without const qualification and corresponding note attached to the type
definition/declaration.

Differential Revision: https://reviews.llvm.org/D135851